This invention relates, in general, to chemical-mechanical polishing processes, and more particularly, to slurries for chemical-mechanical polishing processes.
Processes for manufacturing semiconductor devices often include a chemical-mechanical polishing (CMP) step to improve the planarity of a metal layer. The CMP step uses abrasive particles that are suspended in a colloidal slurry. Different additives or reagents can be combined with the slurry to improve the polishing rate and the selectivity of the slurry. As an example, various ionic salts, such as iron nitrate (Fe(NO.sub.3).sub.3) or peroxide (H.sub.2 O.sub.2), have been used as an oxidizer for metal CMP processes. Other reagents can also be combined with the slurry to improve the transport or Theological properties of the slurry, and still other reagents can be mixed into the slurry to inhibit the corrosion of the surface being polished.
However, with the addition of all the above-described reagents, the colloidal properties of the slurry are degraded. Furthermore, the degree of acidity or basicity (i.e., the pH value), the electrochemical properties, the Theological properties, and the colloidal properties of the slurry are very difficult to control independently. Consequently, the CMP process produces non-uniformly polished surfaces that have many defects.
Accordingly, a need exists for a slurry that provides an appropriate balance between the pH value, the colloidal properties, the electrochemical properties, and the rheological properties of the slurry while exhibiting adequate polishing selectivity between metal and dielectric surfaces, while having efficient transport properties during a CMP process, and while reducing the corrosion of metal surfaces during the CMP process.